[43.01] The Emission Spectrum of the Accretion Column on Her X-1

D.A. Leahy (University of Calgary)

Like many other X-ray pulsars, the pulse shape of Her X-1 is
energy dependent. Since the pulse shape is caused by the
varying line-of-sight to the emission region as the neutron
star rotates, the energy dependence implies a spatially
dependent emission spectrum. Some model for the spatial
structure of the emission region is needed in order to
separate the emission spectrum from different parts of the
emission region.

For Her X-1 the geometry of the emission region has been
well determined (Leahy, 2004, ApJ, 613, 517). This was
possible due to the observed pulse shape evolution caused by
the precessing accretion disk in the system (Scott, Leahy,
Wilson, 2000, ApJ, 539, 392). Only a filled cone shaped
emission fits the observed pulse shape. This model is
described here and is applied to observations of the X-ray
pulse shape at several different X-ray energies. The
emission spectrum of the top surface and of the side surface
of the accretion column are thus derived from observations.
The resulting spectra are compared to some theoretical
calculations of emission from a strongly magnetized plasma.

This work was funded by a grant from the Natural Sciences
and Engineering Research Council of Canada.